Breeding, husbandry, veterinary care, and hematology of marsh rice rats (Oryzomys palustris), a small animal model for periodontitis.

Rice rats (Oryzomys palustris) are a recognized animal model for studying periodontal disease and the photoperiodic regulation of reproduction. Here we share information regarding the breeding, husbandry, veterinary care, and hematologic findings about this animal species to facilitate its use in studies at other research institutions. Rice rats initially were quarantined and monitored for excluded pathogens by using microbiologic, parasitologic, and serologic methods with adult female Mus musculus and Rattus norvegicus sentinel animals. Breeders were paired in a monogamous, continuous-breeding system. Rats were housed in static filter-top cages, maintained on commercial chow under 14:10-h light:dark cycles at 68 to 79 °F (20.0 to 26.1 °C) and 30% to 70% humidity. Rice rats apparently adapt relatively well to standard laboratory conditions, despite their aggressive behavior toward conspecifics and humans. Our analysis of 97 litters revealed that dams gave birth to an average of 5.2 pups per dam and weaned 4.2 pups per dam. Several procedures and biologic reagents normally used in standard laboratory rodents (mice and rats) can be used with rice rats. In addition, we present hematologic and serum chemistry values that can be used as preliminary reference values for future studies involving rice rats.

17ß-Hydroxyestra-4,9,11-trien-3-one (Trenbolone) preserves bone mineral density in skeletally mature orchiectomized rats without prostate enlargement.

Testosterone enanthate (TE) administration attenuates bone loss in orchiectomized (ORX) rats. However, testosterone administration may increase risk for prostate/lower urinary tract related adverse events and polycythemia in humans. Trenbolone enanthate (TREN) is a synthetic testosterone analogue that preserves bone mineral density (BMD) and results in less prostate enlargement than testosterone in young ORX rodents. The purpose of this experiment was to determine if intramuscular TREN administration attenuates bone loss and maintains bone strength, without increasing prostate mass or hemoglobin concentrations in skeletally mature ORX rodents. Forty, 10 month old male F344/Brown Norway rats were randomized into SHAM, ORX, ORX+TE (7.0mg/week), and ORX+TREN (1.0mg/week) groups. Following surgery, animals recovered for 1 week and then received weekly: vehicle, TE, or TREN intramuscularly for 5 weeks. ORX reduced total and trabecular (t) BMD at the distal femoral metaphysis compared with SHAMs, while both TREN and TE completely prevented these reductions. TREN treatment also increased femoral neck strength by 28% compared with ORX animals (p<0.05), while TE did not alter femoral neck strength. In addition, TE nearly doubled prostate mass, compared with SHAMs (p<0.05). Conversely, TREN induced a non-significant 20% reduction in prostate mass compared with SHAMs, ultimately producing a prostate mass that was 64% below that found in ORX+TE animals (p<0.01). Hemoglobin concentrations and levator ani/bulbocavernosus (LABC) muscle mass were elevated in ORX+TE and ORX+TREN animals to a similar degree above both SHAM and ORX conditions (p<0.01). In skeletally mature rodents, both high-dose TE and low-dose TREN completely prevented the ORX-induced loss of tBMD at the distal femoral metaphysis and increased LABC mass. TREN also augmented femoral neck strength and maintained prostate mass at SHAM levels. These findings indicate that TREN may be an advantageous agent for future clinical trials evaluating agents capable of preventing bone loss resulting from androgen deficiency.

A rehabilitation exercise program induces severe bone mineral deficits in estrogen-deficient rats after extended disuse.

OBJECTIVE: Both estrogen and mechanical loading regulate bone maintenance. However, mechanical overload seems less effective in enhancing bone mineral density (BMD) in estrogen-deficient women. The aim of this study was to determine whether estradiol (E2) influences early-phase bone adaptations to reambulation (REAMB) and/or rehabilitation exercises after hindlimb unloading (HLU) of ovariectomized rats. METHODS: Eighty-one 5-month-old female Sprague-Dawley rats were randomized into the following groups: (1) intact controls, (2) ovariectomy (OVX), (3) OVX + E2, (4) OVX + 4 weeks of HLU, (5) OVX + E2 + HLU, (6) OVX + HLU + 2 weeks of quadrupedal REAMB, (7) OVX + E2 + HLU + REAMB, (8) OVX + HLU + REAMB + supplemental climbing, jumping, and balance exercises (EX), or (9) OVX + E2 + HLU + REAMB + EX. Serial dual-energy x-ray absorptiometry scans were performed to track total body bone characteristics throughout the study, and peripheral quantitative computerized tomography was used to determine distal femoral metaphyseal bone mineral characteristics. RESULTS: Total body BMD increased by 4% to 8% in all animals receiving supplemental E2, whereas BMD did not change in animals without E2. OVX reduced trabecular BMD at the femoral metaphysis, and HLU exacerbated this loss while also reducing cortical BMD. E2 protected against OVX + HLU-induced bone loss at the femoral metaphysis. Conversely, REAMB did not alter BMD, regardless of estrogen status. In the absence of E2, REAMB + EX resulted in severe bone loss after OVX + HLU, with trabecular BMD and cortical BMD measurements that were 91% and 7% below those of controls, respectively (P ≤ 0.001). However, in the presence of E2, REAMB + EX did not negatively influence bone mineral characteristics. CONCLUSIONS: E2 protects against bone loss resulting from combined OVX + HLU of rodents. In the absence of estrogen, exercise induces disadvantageous early-phase bone adaptations after extended disuse.

Oncologic doses of zoledronic acid induce osteonecrosis of the jaw-like lesions in rice rats (Oryzomys palustris) with periodontitis.

Though osteonecrosis of the jaw (ONJ) is temporally-associated with the use of nitrogen-containing bisphosphonates (N-BPs), a cause-and-effect relationship has not yet been established. We hypothesize that ONJ is a two-stage process in which: (1) risk factors initiate pathologic processes in the oral cavity that lead to a supranormal rate of hard tissue necrosis; and (2) powerful antiresorptives reduce the rate of removal of necrotic bone sufficiently to allow its net accumulation in the jaw. To test this hypothesis, we used the rice rat model of periodontitis. At age 28 days, rats (n = 15/group) were placed on a high-sucrose and casein diet to exacerbate the development of periodontitis. Animals were injected subcutaneously (SC) biweekly with vehicle or alendronate (ALN, 15 µg/kg), or IV once monthly with vehicle, a low dose (LD) of zoledronic acid (ZOL), or a high dose (HD) of ZOL and sacrificed after 6, 12, 18, and 24 weeks. Mandibles and maxillae were analyzed to determine the effects on the: (1) progression of periodontitis; (2) integrity of alveolar bone; (3) status of bone resorption and formation; (4) vascularity; and (5) osteocyte viability. We found that only HD-ZOL induced ONJ-like lesions in mandibles of rice rats after 18 and 24 weeks of treatment. These lesions were characterized by areas of exposed necrotic alveolar bone, osteolysis, a honeycomb-like appearance of the alveolar bone, presence of bacterial colonies, and periodontal tissue destruction. In addition, inhibition of bone formation, a paradoxical abolition of the antiresorptive effect of only HD-ZOL, increased osteocyte necrosis/apoptosis, and decreased blood vessel number were found after 18 and/or 24 weeks. Our study suggests that only HD-ZOL exacerbates the inflammatory response and periodontal tissue damage in rice rats, inducing bone lesions that resemble ONJ.

17ß-Hydroxyestra-4,9,11-trien-3-one (trenbolone) exhibits tissue selective anabolic activity: effects on muscle, bone, adiposity, hemoglobin, and prostate.

Selective androgen receptor modulators (SARMs) now under development can protect against muscle and bone loss without causing prostate growth or polycythemia. 17ß-Hydroxyestra-4,9,11-trien-3-one (trenbolone), a potent testosterone analog, may have SARM-like actions because, unlike testosterone, trenbolone does not undergo tissue-specific 5α-reduction to form more potent androgens. We tested the hypothesis that trenbolone-enanthate (TREN) might prevent orchiectomy-induced losses in muscle and bone and visceral fat accumulation without increasing prostate mass or resulting in adverse hemoglobin elevations. Male F344 rats aged 3 mo underwent orchiectomy or remained intact and were administered graded doses of TREN, supraphysiological testosterone-enanthate, or vehicle for 29 days. In both intact and orchiectomized animals, all TREN doses and supraphysiological testosterone-enanthate augmented androgen-sensitive levator ani/bulbocavernosus muscle mass by 35-40% above shams (P ≤ 0.001) and produced a dose-dependent partial protection against orchiectomy-induced total and trabecular bone mineral density losses (P < 0.05) and visceral fat accumulation (P < 0.05). The lowest doses of TREN successfully maintained prostate mass and hemoglobin concentrations at sham levels in both intact and orchiectomized animals, whereas supraphysiological testosterone-enanthate and high-dose TREN elevated prostate mass by 84 and 68%, respectively (P < 0.01). In summary, low-dose administration of the non-5α-reducible androgen TREN maintains prostate mass and hemoglobin concentrations near the level of shams while producing potent myotrophic actions in skeletal muscle and partial protection against orchiectomy-induced bone loss and visceral fat accumulation. Our findings indicate that TREN has advantages over supraphysiological testosterone and supports the need for future preclinical studies examining the viability of TREN as an option for androgen replacement therapy.

Dietary dried plum increases bone mass in adult and aged male mice.

Bone is progressively lost with advancing age. Therapies are limited and the only effective proanabolic regimen presently available to restore bone is intermittent treatment with teriparatide (parathyroid hormone 1-34). Recent evidence suggests that dietary supplementation with dried plum (DP) can prevent bone loss due to estrogen deficiency. To determine whether dietary DP supplementation can prevent the loss of bone with aging and whether bone that has already been lost can be restored, adult (6 mo) and old (18 mo) male mice were fed a normal diet or isoenergetic, isonitrogenous diets supplemented with DP (0, 15, and 25% DP by weight) for 6 mo. MicroCT analysis and bone histomorphometry were used to assess bone volume, structure, and metabolic activity before, during, and after dietary supplementation. Mice fed the 0% DP diet (control diet) lost bone, whereas both adult and old mice fed the 25% DP-supplemented diet gained bone. Adult but not old mice fed the 15% diet also gained bone. Cancellous bone volume in mice receiving 25% DP exceeded baseline levels by 40-50%. Trabecular structure varied with diet and age and responses in old mice were generally blunted. Trabecular, but not cortical, mineral density varied with age and measures of bone anabolic activity were lower in aged mice. Our findings suggest that DP contains proanabolic factors that can dramatically increase bone volume and restore bone that has already been lost due to aging. In turn, DP may provide effective prophylactic and therapeutic agents for the treatment of osteoporosis.